#include<iostream>
#include<cmath>
using namespace std;
int main(){
	double a,b,t,x;
	scanf("%lf",&x);
	a=x;
	b=a/2;
	while(abs(a-b)>=0.00001){
		a=b;
		b=(a+x/a)/2;
	}
	printf("%.3lf\n",b);
	return 0;
}
